The use of plates for osteofixation is well known. Plates are used to stabilize, mend, or align a patient's bone. Fasteners such as screws are driven through holes in the plate to secure the plate to the bone. The bone often needs to be drilled to allow the screws to be properly secured. The drilling is done through the holes in the plate to ensure proper alignment of the plate on the bone. Accurate alignment of the holes in the plate and the holes drilled in the bone is crucial to properly affix the plate to the bone. Thus, the plate must be maintained at a specific position on the bone while a hole is drilled and a screw is driven into the bone.
In order to accomplish the bone drilling, a drill guide is employed to ensure proper alignment of the plate hole with the hole drilled in the bone. In some cases, due to limited access, it is necessary to introduce drills and screws through a small incision in the soft tissues covering the site of osteofixation. A cannula is inserted into the soft tissue incision to ensure the opening is maintained, to provide access to the bone for drills and screws, and to provide protection for the surrounding soft tissue. Current cannula systems allow for passage of drill guides, drills, screwdrivers, and screws through a cannula that must be placed and held in alignment with the holes in the plate. Alignment of such cannula systems is accomplished by providing complementary geometry on the plate and the tip of the cannula. This method of alignment, however, requires constant axial pressure on the plate and is difficult to maintain. Relying on axial pressure for alignment makes it particularly difficult to manipulate the plate intraorally in maxillofacial surgery. Releasing axial pressure on the plate can cause the cannula and the plate to become misaligned with respect to the hole being drilled in the bone.